Mastering - Posted on 2016-06-28 by Tyler Stowe

Mastering is the final step in engineering music. Once the mix is completed, the mastering process begins. It is the process of taking and transferring the recorded audio and adding the final touches that all future copies will be made from and distributed. The mastering engineers job is to correct mix balance issues and to enhance sonic characteristics. These engineers have to be sure that there's a consistent sound and that levels match throughout the album. They also have to be sure that the tracks work in relation to each other when played in a sequence. Do the songs volume sound the same? Do they smoothly transition from the end of one to song into the beginning of the next?    

Mastering engineers also determine your songs and albums relative loudness. Relative loudness is an audio term that refers to how loud a song is compared to other songs. It is measured using peak meters and RMS. Peak meters measure volume in real time where RMS measures an average volume for an entire song or performance. In the 80s, the standard RMS level was -18dBFS to -12dBFS. Later in the early 90s, advertisers took advantage of the fact that when people hear things louder, they think it is more important or better than something less as loud. This started what was called the 'Loudness War'. Many bands became aware of this and wanted their albums the loudest. So started the war to see who had the loudest album. The problem with doing this is that in order to get loud sounding songs, their dynamic range had to be reduced. This made the songs flat and boring to listen to.  In the mastering process, audio is run through compresson and limiting that strip away at the songs dynamic range. The engineer then gets an overall volume boost by adding gain at different stages. This makes the quietest parts of a song as loud as the loudest parts.

There's also a technical process that mastering engineers must do to prepare the music to be put on a compact disc. Data is encoded on a CD using what it is called a Linear Pulse Code Modulation(LPCM). This data includes the audio infomation, table of contents, ISRC codes, start and stop times, song titles, and index info. This data is stored on the first two subcode channels of the eight included labeled P,Q,R,S,T,U,V, and W.  Most albums are recorded at a high sample rate and bit depth and need to be bounced down to a lower sample rate and bit depth. Redbook CD standard is 16-bit, 44.1kHz.  This reduces the quality and can really alter the sound. In order to do this safely, dithering was discovered. Dithering is the process that fixes quantization errors by randomizing the amplitude vales of the samples. This causes the samples to be quantized to their nearest values instead of being dropped.

Mastering is an important process that takes years to develope and requires keen hearing to make the most minutiae of changes.